Alternating-current motor.



V v. A. PYNN.

ALTERNATING CURRENT MOTOR.

APPA-JICATION FILED FEB.21,1910.

1,010,135, Patented N0v.28, 1911.

cop? eriron 35 a W/T/VESSES. INVENTOR of Valre A. Fynn VALEBE ALFREDrum, or Lennon, ENGLAND.

ALTERNATING-CURRENT MOTOR.

Specification of Letters Patent.

Patented Nov. 28, 1911.

Application filed February 21, 1910. Serial No. 545,002.

To all whom it may concern:

Be it known that I, VALIERE ALFRED FYNN, a subject of the King ofEngland, residing at London, IV. (1, England, have invented a certainnew and useful Alternating-Current Motor, of which the'following is sucha full, clear, and exact description as will enable any one skilled inthe art to which it appertains to make and use the same, reference beinghadto the accompanying drawings, forming part of this specification.

My invention relates to the induced members of alternating currentmotors and more particularly to those having a permanentlyshort-circuited winding, such as a squirrelcage, together with acommuted winding. This application is a continuation in part of mattercontained in my former application Serial No. 506,955, filed July- 10,1909. It

has been proposed to place the squirrel-cage winding of such motors inslots situated within the zone of those carrying-the commuted windingand separated from the lat ter by a certain radial depth of the rotorlaminations with the object of improving the starting performance. Testshave shown that under such conditions the permanently short-circuitedwinding is practically as ineffective under normal running conditions asit is at starting.

It is the object of my invention to provide between the commuted and thepermanently short-circuited windings, a magnetic shunt or bridge whichwill be inductively responsive to any varying flux tending to threadsaid magnetic shunt or bridge. I therefore so constitute thismagnetic-shunt as to facilitate the formation of Foucault currentstherein, which I utilize to produce a useful screening. effect, 216. todiminish the amount of flux which would otherwise thread this bridge.

The frequencyof the current in each conductor of the permanent-1yshort-circuited winding of a self-excited single-phase shunt inductionmotor is twiceas great in normal operation as it is at the moment ofstarting. The frequency of the self-induced flux surroundingtheseconductors in-normal operation will, therefore, be twice as great as atthe moment of starting. Since' Foucault currents increase with thefrequency then the screening effect of my inductively responsive shuntwill be considerably greater in normal operation than it is at themoment of starting. The self-induction of the permanentlyshort-circuited winding which depends on the amount of flux locallysurrounding it, will, therefore, be relatively large at starting, andsmall in normal operation. A large self-induction of the permanentlyshort-circuited winding at starting is beneficial, inasmuch as acomparatively small induced current in such a winding is then sufficientto force much of the main inducing flux to thread the magnetic shunt andthus link with the commuted winding without linking with the permanentlyshortcircuited winding. A small self-induction of this winding in normaloperation is essential in order to fully utilize the copper on theinduced member and to secure a commercially satisfactory output forweight.

In building rotors for single-phase motors it is necessary in order tosecure an even commercially acceptable efiiciency, tomake use of verythin and very carefully insulated laminations. The main object of such astructure is to reduce the Foucault currents therein to a negligibleamount. This object is so easily attained in practice in the mannerdescribed that the rotor laminations of a commercial single-phase motormay be said to show no inductive response to any varying flux tending tothread them. A

magnetic bridge formed by the rotor lamiis even detrimental to themachine that such be the case. It is only, necessary that a flux shallthread this bridge at starting. Since my magnetic bridge is madeinductively responsive the screening effect will,

'as already explained, be greater in normal operation than at the momentof starting and will thus facilitate the starting (if the motor withoutmaterially impairing its running efficiency.

In the preferred form of my invention, I dispose the commuted and thepermanently short-circuited windings in the same slots, arrange themagnetic material forming my inductively responsive magnetic shunt between the two and conductively secure said magnetic material to thepermanently shortcircuited wmdmg. I thus secure a sound mechanicalconstruction and can take advantage of the conductlvity of the magneticIn the accompanying drawings Figure 1 indicates the preferredarrangement of the windings and the magnetic shunt in the rotor; Fig. 2illustrates one way of securing the inductively responsive magneticshunt to the conductors of the permanently shortcircuited winding; Fig.3 indicates a modified construction of the inductively responsivemagnetic bridge and shows the two rotor windings inseparate but adjacentslots.

In Fig. l the commuted winding 1% and the permanently short-circuitedwinding 36 are shown in the same slots and are separated by aninductively responsive magnetic shunt 35. This magnetic shunt iscomposed of iron or steel strips lying parallel to the active portionsof the rotor conductors, and in electrical contact with each other.bridge therefore consists of one element only inthe electrical sense.The fact that this element is composed of three parts in electricalcontact witheach other merely increases its ohmic resistance in thedirection of the flow of the induced Foucault currents. This bridge ismade more inductively responsive than the rotor laminations by the factthat the smallest dimension of one element of this bridge as measured inthe plane of the induced Foucault currents is greater than the thicknessof one sheet of the rotor laminations.

In Fig. 2 is shown one way of conductively securing the inductivelyresponsive magnetic shunt 35 to the conductors 36 of the permanentlyshort-circuited winding. This winding is here shown as being of thesquirrel-cage type and the magnetic shunt is supposed to consist by wayof example of a solid steel bar 35 of same length as the squirrelcagebars. lhe rivets 40 secure 35 to 36 and to the end rings 41 of thesquirrel-cage. The radial thickness of this bar whose length exceeds thewidth of the rotor laminations is greater than the thickness of onesheet of the rotor laminations and this magnetic shunt is therefore moreinductively responsive than the rotor laminations.

In Fig. 3 the rotor carries a commuted winding 14 and a permanentlyshort-circuited winding 36. They are disposed in alternate slots and theinductively responsive magnetic shunt consists of radially laminatedstrips 35 located in the same slots as 36 and placed above that winding.This shunt consists of one element formed by eight long sheets oflaminations placed on edge and in electrical. contact with each Thisother. It is more inductively responsive than the rotor laminationsbecause its length and its radial width are greater than the thicknessof one sheet of the rotor laminations. Because of the presence of theinductively responsive shunt 35 the self induction of the permanentlyshort -circuited winding 36 will, as previously explained, be smaller innormal operation than at starting and the screening effect of saidwinding will therefore be greater at starting than in normal operationwith the result that much of the main flux will be forced to thread thebridge 35 and will miss the squirrel-cage at starting while stilllinking with the commuted winding, thus improving the startingperformance.

It is well known that the" functions of the rotor and the stator of amotor can be interchanged without modifying the mode of operation of themachine. It will be understood, therefore, that by the word rotor, asused in the specification and claims I mean the induced member of themotor.

I preferto use the rotor described and claimed in this specification inthe type of motor shown for instance in my United States Patents Nos.967,362 and 967,363 dated August 16, 1910.

Having fully described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

l. A laminated rotor having two windings one of which is permanentlyshort-Cir cuited, a magnetic bridge lying above the conductors of thepermanently short-circuitedwinding, said magnetic bridge having at leastone element whose dimension in the direction parallel to the rotor shaftis greater than the thickness of the rotor laminations.

2. A laminated rotor having a commuted winding, a permanentlyshorteireuited winding and a magnetic bridge lying above the conductorsof the permanently short-circuited winding, said magnetic bridge havingat least one element whose dimension in the direction parallel to therotor shaft is greater than the thickness of the rotor laminations.

3. A rotor having a commuted winding and a squirrel-cage winding in thesame slots, said commuted winding lying above the squirrel-cage winding,and a magnetic bridge inductively responsive to a part of the fluxlinking with the conductors of the squirrel cage winding, said magneticbridge lying above said conductors.

4. A laminated rotor having a commuted winding, a permanentlyshortcircuited winding. and a magnetic bridge lying above the conductorsof the permanently shortcircuited winding, said bridge having at leastone element whose length approximately equals the width of the rotor.

5. A laminated rotor having a commuted my hand and affixed my seal inthe presence winding, a permanently short circuited of two subscribingwitnesses. winding, and an inductively responsive magnetic bridge lyingabove the conductors of YALERE ALFRED FYNN' the permanentlyshort-circuited winding Witnesses: and in electrical contact therewith.E. E. HUFFMAN,

In testimony whereof, I have hereunto set A. C. FOWLER.

